1. Field of Endeavor
The present invention relates to devices, systems, and processes useful for the treatment of apnea.
2. Brief Description of the Related Art
Breathing and Sleep
I. Breathing Background
Breathing consists of taking air into the lungs, or inhalation, and expelling air from the lungs, or expiration. Normally, inspiration is an active process requiring various muscles to contract while expiration is passive, a recoil from energy previously stored in muscles, ligaments, and tendons during inspiration.
Breathing is orchestrated by the brain which integrates emotional, chemical, and physical stimuli to regulate air movement into and out of the lungs. Regulation is controlled through the activation of motor nerves originating in the brain (cranial nerves or CN) and from nerves whose bodies are in the spinal cord. When recruited, these nerves cause various muscles to contract or to remain relaxed. In humans, quiet breathing occurs primarily through the cyclical stimulation of the muscles of the two hemi-diaphragms.
Breathing is under conscious and unconscious control. With an intact brain, an individual can take or not take a breath when ever desired. Singers and wind instrument musicians control breathing consciously to make music; swimmers gulp in a full lung of air in a second. Voluntary control of breathing originates in the cerebral cortex, although, in the extreme, various chemo-receptor reflexes are capable of overriding conscious control.
However, most of the time breathing is unconsciously controlled by specialized centers in the brainstem, which automatically regulate the rate and depth of breathing to match the body's needs at any given time. In addition to involuntary control of breathing by these respiratory brain centers, breathing is unconsciously influenced by a person's emotional state, by way of inputs from the limbic system, and by ambient temperature, by way of the hypothalamus.
Breathing rate and depth of breathing is tightly controlled by the brain. Changes in rate and depth of breathing are determined primarily by blood levels of carbon dioxide and secondarily by low or very low blood concentrations of oxygen. Chemo-receptors associated with three arteries, the carotid bodies at both carotid bifurcations and in the aortic arch, respond to changes in the blood concentration oxygen and carbon dioxide. Afferent neurons from the carotid bodies and aortic bodies reach the brain by way of the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X), respectively.
Levels of CO2 rise in the blood when the metabolic consumption of O2 is increased beyond the capacity of the lungs to expel CO2. CO2 is stored in the blood primarily as bicarbonate (HCO3—) ions, first by conversion to carbonic acid (H2CO3) through the enzyme carbonic anhydrase, and then by disassociation of this acid into H+ and HCO3—. Build-up of CO2 therefore causes an equivalent increase in hydrogen ion concentration. By definition, an increase in blood hydrogen ion concentration is a decrease in blood pH. A drop in blood pH stimulates the chemo-receptors in the medulla oblongata and the pons, in the brain.
When the brain senses that carbon dioxide concentration is high, that pH is low, and that oxygen concentration is low, it sends nerve impulses through the phrenic and thoracic nerves, respectively, to the muscles of the diaphragms and the intercostal muscles, through the hypoglossal nerve (CN XII) to the muscles of the tongue, and through the recurrent laryngeal nerve (a branch of CN X) to the muscles of the larynx. These and other nerve impulses cause the hemi-diaphragm muscle to contract, inhibits contraction of the intercostal muscles, and cause the complex muscles in the pharynx to contract. Contraction of the hemi-diaphragm muscles cause the volume to the thoracic cage to increase. Since the volume of the lungs does not instantly increase with a change in volume of the thorax, a transient drop in intra-thoracic (and intra-pleural and intra-esophageal) pressures occurs. Decreased intra-thoracic pressure causes the volume of the lungs to expand, which causes air to enter the nostrils and/or mouth, to flow through the nasopharynx and oropharynx, the laryngopharynx, the larynx, the trachea, the bronchi, and, finally, the alveoli.
Mouth breathing refers to the state of inhaling and exhaling primarily through the mouth. A healthy individual normally breathes through the nose while resting or doing light exercise, and breathes simultaneously through both the nose and mouth during vigorous aerobic exercise, in order to supply sufficient oxygen for metabolic needs. Excessive mouth breathing causes problems because air is not filtered and warmed as much as when it is inhaled through the nose, as it bypasses the nasal canal and paranasal sinuses, and dries out the mouth. Mouth breathing is often associated with congestion, obstruction, or other abnormalities of the nasal passage ways. Everyone mouth breathes when the nose is stopped up by a cold. Mouth breathing is associated with obstructive sleep apnea.
The phayrnx is a complex fibromuscular tube which extends from the base of the skull to the origin of the esophagus. Portions of the pharynx lie posterior to the nasal cavity (nasal pharynx), oral cavity (oral pharynx), and larynx (laryngeal pharynx). The oral pharynx and laryngeal pharynx are shared for breathing and eating.
The muscular walls of the pharynx are formed of an outer layer made up of three circularly disposed muscles, the constrictors, and the inner muscular layer of the pharynx is made up of three small, longitudinally oriented muscles. During swallowing, successive contraction of the superior, middle, and inferior constrictor muscles helps to propel a bolus ball of food down into the esophagus. In addition, contraction of the three longitudinal muscles of the pharynx helps to raise the pharynx, effectively aiding it in engulfing the bolus of food.
The pharynx contains a “ring” of specialized lymphatic tissue designed to prevent the entry of pathogens into the digestive and respiratory tracts. This specialized lymphatic tissue is known as “tonsils” and is organized into three groups: nasopharyngeal tonsils (adenoids), located in the nasal pharynx; palatine tonsils (tonsils), located between the palatoglossal and palatopharyngeal folds in the oral pharynx; and lingual tonsils, located on the posterior surface of the tongue.
Fresh air in the alveoli presents high gaseous oxygen concentration and low gaseous carbon dioxide concentration to blood in the proximal pulmonary capillaries. Carbon dioxide moves from the blood in the proximal pulmonary capillaries to air in the alveoli (carbon dioxide is “blown off”) and oxygen moves from air in the alveoli to hemoglobin molecules in the blood of the proximal pulmonary capillaries. “Blue blood” in the proximal pulmonary capillaries becomes saturated, or “red blood”, in the distal segments of these capillaries. Relaxation of the intercostals muscles, contraction of the muscles of the hemi-diaphragms, contraction of the muscles of the tongue, and relaxation of the muscles of the pharynx is a complex neuromuscular orchestration that occurs with each normal breath.
In addition, breathing centers in the medulla and pons integrate neural signals. The reticular formation, the nucleus retroambigualis, nucleus ambiguus, nucleus parambigualis, and the pre-Botzinger complex control voluntary forced exhalation and augment the force of inspiration. The nucleus tractus solitarius controls the timing of inspiratory movements. The pneumotaxic center fine tunes breathing rate, and the apneustic center in the lower pons controls breathing intensity. Further breathing integration occurs in the anterior horn cells of the spinal cord.
II. Sleep Apnea
“Apnea” is the technical term for suspension of breathing. During apnea there is no movement of the muscles of breathing and the volume of the lungs initially remains unchanged. Depending on the openness of the airways there may or may not be a flow of gas between the lungs and the environment. Apnea can be voluntarily achieved through breath-holding, drug-induced, mechanically induced (as in strangulation or obstructive sleep apnea), and caused by brain or spinal cord disease or injury (as in central sleep apnea).
II.A. Definition of Sleep Apnea
Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. Each apneic event lasts long enough so that one or more breaths are missed. Missed breaths occur repeatedly throughout sleep. Sleep apnea is definitively diagnosed with an overnight sleep test called a “polysomnogram.” An apneic event includes an absence of air flow for 10 second or longer, with either a neurological arousal (a 3-second or greater shift in EEG frequency) or a blood oxygen desaturation of 4% or greater, or both.
In addition to complete cessation of breathing, individuals with sleep apnea also exhibit smaller than normal breaths or “hypopneas.” Hypopneas in adults are defined as a 50% reduction in air flow that occurs for more than 10 seconds, followed by a 4% desaturation in blood oxygen or neurological arousal, or both. Since both apneas and hypopneas are detrimental to sleep, the Apnea-Hypopnea Index (AHI) was created to measure the overall severity of sleep apnea by counting the number of apneas and hypopneas that occur per hour of sleep. The categorization of normal and abnormal states is shown in Table I.
TABLE IApenea-Hypopnea Index (AHI)AHIRating <5Normal 5 to 15Mild15 to 30Moderate>30Severe
II.B. Signs and Symptoms of Sleep Apnea
1. Frequent cessation of breathing (apnea) during sleep often noticed by one's sleep partner.
2. Choking or gasping during sleep to get air into the lungs
3. Loud snoring
4. Sudden awakenings to restart breathing
5. Waking up in a sweat during the night
6. Feeling fatigued in the morning after a night's sleep
7. Headaches, sore throat, or dry mouth in the mornings after waking up
8. Exaggerated daytime sleepiness, including falling asleep at inappropriate times, such as during driving or at work
Individuals with sleep apnea are rarely aware of having difficulty breathing, even upon awakening. Sleep apnea is recognized as a problem by others witnessing the individual during episodes or is suspected because associated abnormalities seen elsewhere in the body. Symptoms may be present for years, even decades without identification, during which time the sufferer may become conditioned to the daytime sleepiness and fatigue associated with significant levels of sleep deprivation.
II.C. Risk factors of Sleep Apnea
1. Nasal, oral, pharyngeal, or laryngeal anatomic or physiologic abnormalities including large tonsils or adenoids, chronic nasal congestion, deviated nasal septum, enlarged tongue, receding chin, enlarged soft palate, or lengthened uvula.
2. Excess fat deposit surrounding the pharynx
3. Family history of sleep apnea
4. Old age
5. Male gender (1, 2)
II.D. Sequela of Sleep Apnea
Mild, occasional sleep apnea, such as many people experience during an upper respiratory infection, may not be important. However, chronic, severe obstructive sleep apnea requires treatment to prevent sleep deprivation and other medical complications, including death.
II.D.1. Sleep Deprivation
Both the person with sleep apnea and the bed partner suffer from sleep deprivation. A bed partner may lose an hour or more of sleep each night from sleeping next to a person with sleep apnea. Along with the apnea episodes, the person afflicted with sleep apnea may have additional trouble sleeping caused by side effects of the condition, including a frequent need to get up and urinate during the night, and excessive nighttime sweating.
II.D.2. Oxygen Deprivation
When you stop breathing, your brain does not get enough oxygen. Drastic problems can result from the oxygen deprivation of sleep apnea, including premature death.
In some individuals, elevated systemic arterial pressure (commonly called high blood pressure) is a sequela of obstructive sleep apnea syndrome(3) When high blood pressure is caused by OSA, it is distinctive in that, unlike most cases of high blood pressure (so-called essential hypertension), the pressure readings do not drop significantly when the individual is sleeping.(4) OSA is associated with signs of cardiac ischemia and cardiac rhythm disturbances. (5). Stroke and even premature death are associated with obstructive sleep apnea.(6)
Individuals suffering from OSA show brain tissue loss in regions that help store memory, thus linking OSA with memory loss.(7)
II.D.3. Metabolic Imbalances
Obstructive sleep apnea is associated with a range of metabolic abnormalities. (8-18). For example, the hormone adiponectin is decreased in concentration in the serum in patients with sleep apnea. This hormone affects: glucose flu; gluconeogenesis; glucose uptake; lipid catabolism; b-oxidation; triglyceride clearance; insulin sensitivity; and protects endothelium from artherosclerosis.
II.D.4. Depression
Approximately one in five people who suffer from depression also suffer from sleep apnea, and people with sleep apnea are five times more likely to become depressed. Existing depression may also be worsened by sleep apnea. Treating sleep apnea may alleviate depression in some people.
II.E. Types of Sleep Apnea
There are three distinct forms of sleep apnea: obstructive; central; and mixed, which is a combination of the two. These three types comprise 84%, 0.4%, and 15% of cases, respectively.(19) Clinically significant levels of sleep apnea are defined as five or more episodes per hour of any type of apnea as identified on a polysomnogram. In obstructive sleep apnea, breathing is interrupted by a physical block to airflow despite contraction of the hemi-diaphragms. Breathing is interrupted by the absence of effort in central sleep apnea. In mixed sleep apnea, there is a transition from central to obstructive features during the apneic events themselves.
III. Obstructive Sleep Apnea (OSA)
The clinical picture of obstructive sleep apnea was first characterized as a personality trait and called the “Pickwickian syndrome.” This term was coined by the famous early 20th Century physician, William Osler, to match the description of Joe, “the fat boy” in Dickens's novel, The Pickwick Papers. Dickens's description is an accurate clinical picture of the adult obstructive sleep apnea syndrome.
The early reports of obstructive sleep apnea in the medical literature described individuals who were very severely affected, often presenting with severe hypoxemia (low O2), hypercapnia (increased CO2) and congestive heart failure. Tracheostomy was the recommended treatment. Though it could be life-saving, post-operative complications in the tracheostomy stoma were frequent in these very obese and short-necked individuals. That a tracheotomy can effectively treat even severe obstructive sleep apnea implies that the anatomic site or sites of obstruction of the airway during sleep are above or superior to the level of the trachea. Historically, however, tracheostomies have involved the implantation of devices inside the trachea, which impedes air movement and can induce other complications.
III.A. Sites of Obstruction
Obstruction of the airway at the level of the nasal cavity, the anterior tongue, the bony jaw, the tonsils, and the adenoids are relatively straightforward to diagnose and can often be accurately identified clinically. The real difficulty in obstructive sleep apnea is identifying the level of obstruction in the pharynx during sleep. Normally, muscles in the body relax during sleep, including those of the pharynx. When relaxed the pharynx is composed of collapsible walls of soft tissue which can obstruct breathing. During each breath, the muscles of the pharynx contract in a coordinated fashion to “open” the pharynx and allow air to flow through.
The pharynx can be identified by lateral radiography, computed tomography (CT), magnetic resonance imaging (MRI), and fluoroscopy.(20) Of these modalities, CT and MRI provide cross sectional images and are the most accurate measurements of pharyngeal narrowing.
III.A.1. Oropharynx
Many studies of patients with obstructive sleep apnea have placed the primary locus of obstruction in the oropharynx. (21-25)
III.A.2. Nasopharynx
Other studies place the primary site of pharyngeal narrowing superior to the oropharynx. (26, 27)
III.A.3. Diffuse
Still others have found that pharyngeal obstruction can be at one location in one individual and at another location is a different person.(28-31)
III.B. Treatment
III.B.1. Minor Treatments
III.B.1.a). Lifestyle Changes
Alcohol avoidance, cessation of the use of muscle relaxants and sleep medications, weight loss, and quitting smoking may each diminish the severity of obstructive sleep apnea. Life style changes are most effective in patients with mild obstructive sleep apnea.
III.B.1.b). Dental Appliances
Some people benefit from various kinds of oral appliances to keep the upper airway open during sleep. An oral appliance is a custom made mouthpiece that shifts the jaw forward to help keep the pharynx open during sleep. Oral appliance therapy is usually successful in patients with mild to moderate obstructive sleep apnea.
III.B.1.c). Sleep Posture
Many people benefit from a change of sleep posture.(32-37) For example, sleeping at a 30 degree elevation of the upper body or higher, or sleeping on one's side, may help to prevent the gravitational collapse of the phayrngeal airway.
III.B.1.d). Medication
Medications like Acetazolamide lower blood pH and encourage breathing. Low doses of oxygen are also used as a treatment for hypoxia.
III.B.1.e). Wind Instruments
A recent study found that learning and practicing the didgeridoo wind instrument helped reduce snoring and sleep apnea, as well as daytime sleepiness. This appears to work by strengthening muscles in the upper airway, thus reducing their tendency to collapse during sleep.(38)
III.B.2. Major Treatments
III.B.2.a) Continuous Positive Airway Pressure (CPAP)
III.B.2.a).(1) CPAP Benefits
The management of obstructive sleep apnea was revolutionized with the introduction of continuous positive airway pressure by Sullivan.(39-42) The first models were bulky and noisy but the design was rapidly improved and, by the late 1980s, CPAP was widely adopted. The availability of an effective treatment stimulated an aggressive search for affected individuals and led to the establishment of hundreds of specialized clinics dedicated to the diagnosis and treatment of sleep disorders. The vast majority of patients who attend a sleep clinic suffer from a sleep apnea.
III.B.2.a).(2). CPAP Failures
Though CPAP therapy has brought relief from obstructive sleep apnea to many, it is not without complications. Table II lists the common complaints made by patients on CPAP therapy.
TABLE IICommon problems reported with nasal continuous positive airway pressure andtrouble-shooting guideProblem ComplexPossible CauseCorrectionMask Leaks1. Strap adjustment too1. Readjust headgear straps. The maskSkin Irritationloose or too tightshould be as loose as possible while stillPressure sores or blisters2. Incorrect mask sizecreating a seal3. Worn-out mask2. Consult respiratory therapist for a mask4. Dirty maskfitting. Nasal pillows or full-face mask mayprovide a better fit3. Inspect mask for stiffness, cracks orbreaks. Replace mask if needed4. Wash mask daily; wash face nightlyDry nose and/or throat.1. Dry air1. Try nasal saline spray before bedtime andNasal Congestionupon awakeningEpistaxis2. Add heated humidification3. Try topical nasal steroid preparation orantihistamines4. May have some desensitization over time5. Consult physician if symptoms persistDry mouth1. Sleeping with mouth1. Try a chin strapopen2. If this is not helpful, a full-face maskmay be considered3. Add heated humidificationSore, dry, irritated or1. Mask leaks1. Try reseating the mask on the faceswollen eyes,2. Mask too tight2. Readjust headgear straps.conjunctivitis3. Inspect mask for stiffness, cracks orbreaks. Replace mask if needed.4. Use an eye patchRhinorrhea1. Dry air1. Try saline nasal spray before bedtime2. Try topical nasal steroid preparation orintranasal ipratropium bromide beforebedtime3. Add heated humidificationAllergic rhinitis1. Irritants drawn in with1. Place unit on bedside table to keep dustroom air through machineand/or animal hairs out of machine2. Consult respiratory therapist: a fineparticulate filter can be added to some units3. Add heated humidification4. Consult physician if symptoms persist(may require medication)Chest discomfort1. Pressure requirement1. Try pressure ramp at beginning of sleepAerophagiamay be lower atperiodSinus discomfortbeginning of sleep period2. Reduce pressure with bilevel positiveDifficulty exhaling2. Initial adjustmentairway pressureperiod3. Try to reduce pressure requirement byusing oral appliance and CPAP (no dataavailable)CPAP unit too noisy1. Blocked air intake1. Check if air filter is clean and not2. Too close to sleepingblocked by outside itemsarea2. Add a length of hose and place unitfarther awayBed partner intolerance1. Multiple factors (noise,1. Promote education of the patient and bedanxiety)partner2. Recommend attending a patient supportgroup (i.e., A.W.A.K.E. Network of theAmerican Sleep Apnea Association)
III.B.2.b). Surgery
Specific types of surgery can increase the size of the pharyngeal, oral, and nasal airways by removing or reshaping tissues. (43) A surgeon may remove tonsils, adenoids, or excess tissue at the back of the throat or inside the nose. A surgeon may even reconstruct the jaw to enlarge the pharynx.
IV. Central Apnea
Any individual, no matter how healthy, when given enough of a central respiratory depressant, will develop central apnea. In large amounts, alcohol is a central respiratory depressant, and so are opiates, barbiturates, benzodiazepines, and many other tranquilizers and sleep aids.
Central sleep apnea (CSA), the rarest type of sleep apnea, occurs when the brain signals that instruct the body to breathe are delayed. This central nervous system disorder can be caused by disease or injury involving the brainstem, such as a stroke, a brain tumor, a viral brain infection, or a chronic respiratory disease. People with CSA seldom snore, which makes it even harder to diagnose as they do not fit the “normal” profile of a sleep apnea sufferer. However, while the causes of the breathing cessation are different in central sleep apnea and obstructive sleep apnea, the symptoms and results are much the same. Patients are deprived of oxygen and repeatedly awaken at night. The treatments for CSA include specific medications that stimulate the need to breathe and administrations of oxygen.
Central sleep apnea usually occurs most commonly in people who are seriously ill. For example, it can occur in people with a variety of severe and life-threatening lower brain stem lesions. Since the brainstem controls breathing, any disease or injury affecting it may result in apnea, even when awake.
Conditions that can cause central sleep apnea include:
1. Bulbar poliomyelitis
2. Encephalitis affecting the brainstem
3. Neurodegenerative illnesses
4. Stroke affecting the brainstem
5. Cervical spine injury
IV.A. Definition
In pure central sleep apnea, the brain's respiratory control centers do not function normally during sleep. The concentration of carbon dioxide in the blood and the neurological feedback mechanism that monitors it do not react quickly enough to maintain an even respiratory rate, with the entire system cycling between apnea and rapid breathing (hyperpnea), even during wakefulness. The sleeper stops breathing, and then starts again. There is no effort made to breathe during the pause in breathing; there are no chest movements and no struggling. After an episode of apnea, breathing may be faster for a period of time, a compensatory mechanism to blow off carbon dioxide and absorb more oxygen.
The immediate effects of central sleep apnea on the body depend on how long the failure to breathe endures. At worst, central sleep apnea may cause sudden death. Short of death, drops in blood oxygen may trigger seizures—even in the absence of epilepsy. In people with epilepsy, the hypoxia caused by apnea may trigger seizures that had previously been well controlled by medications. In other words, a seizure disorder may become unstable in the presence of sleep apnea. In adults with coronary artery disease, a severe drop in blood oxygen level can cause angina, arrhythmias, or myocardial infarction. Longstanding recurrent episodes of apnea, over months and years, may cause an increase in carbon dioxide levels that can change the pH of the blood enough to cause a metabolic acidosis.
IV.B. Treatment
IV.B.1. Stop CNS Depressant Drugs
IV.B.2. Pace the Diaphragms
When central apnea is severe, the diaphragm can be artificially paced with electrical currents (Synapse Biomedical, Inc, Oberlin, Ohio). Surgically implanted electrodes electrically stimulate the phrenic nerve or the muscles of the hemi-diaphragms, directly. Wires from the electrodes in the diaphragm run to and from a control box worn outside the body. The pacing is performed according to a reconditioning program in which the duration and frequency of electrode stimulation is gradually increased until full-time diaphragm pacing is achieved. When the electrodes are stimulated by current, the diaphragm contracts and air is sucked into the lungs (inspiration). When the electrodes are not stimulated, the diaphragm relaxes and air moves out of the lungs (expiration).
V. Mixed Apnea and Complex Sleep Apnea
Some people with sleep apnea have a combination of obstructive and central sleep apnea. (19) When obstructive sleep apnea is severe and longstanding, episodes of central apnea sometimes develop. The exact mechanism of the loss of central respiratory drive during sleep in obstructive sleep apnea is unknown.
Complex sleep apnea has recently been described by researchers as a novel presentation of sleep apnea. Patients with complex sleep apnea exhibit OSA, but upon application of positive airway pressure, the patient exhibits persistent central sleep apnea. This central apnea is most commonly noted while on CPAP therapy, after the obstructive component has been eliminated.
VI. Conclusion
What is needed in sleep apnea is an integrated medical device system that can treat all forms of sleep apnea with minimal interference with a person's night-time sleeping experience.
Two primary problems exist for patients with sleep apnea: absence of breathing effort and obstruction of air flow. Absence of breathing effort can be treated with electrical pacing of the diaphragm. Obstruction of air flow can be treated with bypass of the pharynx, oral cavity, and nasal cavity airways, as in the creation of a tracheostomy, or by briefly opening obstructive zones within the upper airway with electrical stimulation of the muscles at the site or sites of obstruction. To be effective, the pacing of the diaphragms and the pacing of upper airway muscle contractions would have to be coordinated. The pacing of the diaphragms and bypass of the upper airway would not have to be coordinated.